In fact, it is actually a myth that the Great Wall of China is visable from the moon.

The following got printed in New Scientist Last Word.

Quote:

A person with perfect eyesight is able to resolve up to about one minute of arc without binoculars or a telescope. The Great Wall of China is, very approximately, 20 feet (6 metres) wide. This means that it is not directly visible above about 70,000 feet (20Km), or just over twice the height of Mount Everest. Even if its shadow is taken into account, this would only make it visible, in places, up to perhaps about 200,000 feet (60km) at the most which, because of atmospheric drag, is still below the height necessary for a stable orbit.

Dinkie - It's hard to tell sometimes how puzzles will go over - I've written some that I've thought were completely diabolical that were solved in a question or two, and others that I noted as "Quickies" that took forever -- just depends what track everyone gets on. I look forward to your next puzzle!